Electromagnetic Radiation.

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Electromagnetic Radiation.

The electromagnetic spectrum is the continuum of all electromagnetic waves arranged according to their frequency and wavelength.    The spectrum is divided into regions based on their wavelength and proportionate energy.    At the bottom of the spectrum are Gamma rays, which have the shortest wavelengths (less than 1x10^-12 m), and radio waves at the apex of the spectrum with extraordinarily long wavelengths that exceed a kilometre in length.    While nearly all electromagnetic waves are invisible, there is a visible section that makes up, what normal people know as the colour spectrum.

The sun, earth and other astrophysical bodies radiate electromagnetic energy in the form of a wave.    These waves are given the name ‘electromagnetic’ because they are transmitted as a combination of varying electric and magnetic fields.      These sinusoidal waves travel at right angles to each other and all at the same speed of  3x10^8 m/s in a vacuum.    

(electromagnetic wave)

The fundamental behaviors of all the components of the electromagnetic spectrum are the same.   The most obvious scientific difference is their varying wavelengths and frequencies and in the devices used to generate and detect them.      All electromagnetic waves exhibit diffraction and interference as well as reflection and refraction.     They also all obey the following equation:

V = f.λ

(where v = velocity,  f = frequency, λ = wavelength)

Using this equation and because ‘v’ is a constant for a given medium, we discover that as the wavelength is decreased, the frequency is increased.

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There are seven main sections of the electromagnetic spectrum.  They are, in ascending order of wavelength (where λ represents wavelength):

  • Gamma Rays ( λ = approx. 0.01 nm)

These rays are emitted by certain radioactive nuclei and are the most penetrating and energetic.

  • X – Rays (λ = 10 nm – 10-2  nm)

These rays are produced by bombarding a surface with very fast electrons.

  • Ultra Violet Rays (λ = 380 nm – 60 nm)

These rays come from very hot bodies such as the sun or from electrical discharges through gases.

  • The Visible Spectrum (λ = 400 nm (violet) – 700 nm (red))

This is the only part of the spectrum visible to the naked eye.

  • Infrared (λ = 10-4 m – 10-6 m)

Bodies at below 500°C that are not glowing, radiate these electromagnetic rays.

  • Microwaves (λ = 1mm – 30cm)

These rays are used in radar and microwave ovens.

  • Radio Waves (λ = approx. 100 m)

There are three types of radio waves: FM, shortwave and AM.

(The Electromagnetic Spectrum)

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All electromagnetic rays travel at the same velocity in a vacuum and exhibit the same fundamental behavior.    Infrared and ultraviolet radiation are two perfect examples to compare.   Both travel at the same speed in a vacuum and as an electromagnetic wave and they similarly generate ‘heat’ (they make our skin feel warm when in contact with it).      Conversely, both rays have unique wavelengths and frequencies as well as different methods of creation.    Infrared radiation is emitted by anything we consider ‘glowing red’ with heat, such as hot embers and an electric hot-plate and occurs when molecules inside a material begin to vibrate and rotate.    Ultraviolet radiation is produced mainly from sun and the experimental discharges of an electric arc.    

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The 20th century saw the beginning of the Theory of Quantum Physics.  Up until this time electromagnetic radiation was considered purely as waves that shared many characteristics with light.   However, when it was seen that electricity could be produced by light striking a metal, Albert Einstein hypothesized that radiation exhibited the characteristics and nature of a particle.   Einstein suggested that light behaves like concentrated packets of energy which he called ‘light quanta’ (now referred to as photons).  Scientists believed that these packets of energy could be transmitted by the translation of particles that have momentum and ...

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